As shown in FIG. 6, an impeller 81 used for a rotary machine such as a centrifugal compressor includes a disc 82, blades 83, and a cover 84.
The disc 82 in this impeller 81 includes a cylindrical portion 82a and an annular disc portion 82b that are molded integrally. The cylindrical portion 82a is externally fitted to a rotating shaft. The annular disc portion 82b protrudes from a portion at one side (a right side in FIG. 6) in an axis line O direction on an outer peripheral surface of the cylindrical portion 82a to an outer side in a radial direction. A plurality of blades 83 are arranged at intervals in a circumferential direction on a surface at the other side (a left side in FIG. 6) in the axis line O direction of the annular disc portion 82b. Further, the cover 84 is integrally attached to cover the blades 83 from the other side in the axis line O direction.
In such an impeller 81, a portion on the other side in the axis line O direction on an inner peripheral surface of the cylindrical portion 82a of the disc 82 is integrally fixed to the rotating shaft by being shrink-fitted to the rotating shaft. As only the portion on the inner peripheral surface of the cylindrical portion 82a is shrink-fitted in this way, attachment and detachment of the impeller 81 to or from the rotating shaft can be easily performed. Further, a shrink fitting place is spaced from a center of gravity of the impeller 81. As a result, it is possible to prevent the impeller 81 from deviating from the rotating shaft due to centrifugal force at the time of rotation.
A scheme of individually molding the disc 82, the blades 83 and the cover 84 and then integrating these members through welding is known as a method of manufacturing the impeller 81. However, in the method of manufacturing the impeller 81, welding distortion, a welding defect or the like may occur.
In contrast, a manufacturing method of integrally molding the disc 82, the blades 83 and the cover 84 by performing a cutting process on an impeller material as a base material using a machining tool 90 has been proposed.
Further, for example, a method of manufacturing an impeller by diffusion-bonding an inner peripheral side part and an outer peripheral side part that have formed a flow path between blades, in such a manner that the flow paths are connected to each other, has been proposed in Patent Document 1.